Elucidating the hypoxia-inducible factor (HIF-1) response in gut barrier dysfunction and distant organ damage is the overall objective of this proposal. The studies proposed in this grant will test the following global hypothesis that persistence of the ischemia-induced HIF-1alpha response by intestinal bacteria and their products shifts the HIF-1alpha response from an adaptive/protective response to a potentially maladaptive/injurious one. Consequently, in this proposal, we will test the concept that the sustained HIF- 1cc response in the gut acts as an effector in ischemia/reperfusion-mediated gut injury and the production of gut derived factors, thereby playing a role in gut-induced distant organ damage. By providing potentially important mechanistic information on the pathogenesis of T/HS-induced gut injury, the results obtained from our studies will help clarify key issues of the Center Grant's first global hypothesis, which is that gut-derived factors present in the mesenteric lymph of the ischemic gut contribute to distant organ injury. Additionally, the experiments proposed in our Specific Aims will contribute to the Center Grant's second major hypothesis by testing whether the resistance of proestrus female rats to T/HS-induced gut injury is associated with a differential HIF-1 intestinal response and that the intestinal HIF-1 response to T/HS is. at least in part. modulated by sex hormones. Aim 1 will elucidate the functional significance of l/R-mediated elevations of intestinal HIF-1 in vivo as well as the role of intestinal bacteria in prolonging the intestinal HIF-1 response. The effects of T/HS-induced gut injury, gut inflammation and acute lung injury will be examined in partially deficient HIF-1alpha+/- and HIF-1+/+ WT mice. To further evaluate the effect of intestinal bacteria on the HIF-1 response, intestinal antibiotic decontamination and bacterial overgrowth male rat T/HS models will be employed. The effects of partial HIF-1alpha deficiency on gut injury and inflammation will also be tested in the intestinal bacterial overgrowth and antibiotic decontaminated T/HS models. Aim 2 will test whether overexpression or inhibition of HIF-1 in enterocytic cell lines affects gut barrier function and gut inflammation utilizing enterocytic cell lines. Aim 3 will elucidate the mechanisms by which enteric bacteria or LPS regulate HIF-1 activation in enterocytes under normoxic conditions. Specifically, experiments will determine whether regulation of HIF-1 is via the activation of MARK, Akt or NO. Aim 4 will test the hypothesis that the resistance of proestrus female rats to T/HS-induced gut injury is associated with a blunted intestinal HIF-1 a response. A deeper insight of the intestinal HIF-1 response will identify potential targets for therapeutic intervention at the onset of intestinal ischemia.